A potentiometer as recited above is known from the applicant's own earlier German patent application P 37 31 328.2 which is not a prior publication. In that case two potentiometer halves were made by injection molding to provide an absolutely liquid-tight potentiometer, both halves of the potentiometer containing respective functional elements of the potentiometer. These two potentiometer halves were welded together by an ultrasonic process.
The potentiometer thus obtained indeed is absolutely impermeable to liquids and lends itself to substantially automatic production. Yet it is rather complicated in structure because of the two halves and expensive to manufacture. In particular, a great many working steps are needed to produce it and that in turn requires expensive means of production.
It is, therefore, an object of the invention to improve the potentiometer of the kind specified initially such that its structure will be simpler, whereby it can be produced fully automatically at a reduced number of working steps.
This object is met, in accordance with the invention, in that the rotary engagement piece is made in one piece and embraces the resistor plate and the slider spring.
Advantageous modifications and further developments of the invention may be gathered from the claim. One claim specifies a manufacturing method for the fully automatic production of the potentiometer according to the invention from band material by a multiple unit procedure.
It is an essential advantage of the invention that the potentiometer can be made fully automatically in an injection molding machine using an injection molding tool which accomplishes not only the injection molding proper but also such additional tasks as the punching out of individual pieces from the tape material and the bending of lugs. Manual handling thus no longer is required in the assembly. Instead, three bands or belts are fed stepwise through the injection molding machine.
The potentiometer obtained by such procedure is of simple structure and very sturdy and can be made completely liquid-tight in a very simple way, namely by inserting a sealing ring. Although the structure and manufacturing process of the potentiometer according to the invention thus clearly are simpler than in the case of the potentiometer according to the earlier patent application P 37 31 328.2 the advantages of the earlier potentiometer still are fully maintained. The following advantages should be mentioned specifically:
sealed against liquids, PA1 torques exactly reproducible for the rotational operation of the rotary engagement piece, and PA1 sealing function and torque independent of dimensional tolerances of the individual elements and injection mold.